In-plane Theory of Non-Sequential Triple Ionization

We describe first-principles in-plane calculations of non-sequential triple ionization (NSTI) of atoms in a linearly polarized intense laser pulse. In a fully classically correlated description, all three electrons respond dynamically to the nuclear attraction, the pairwise e-e repulsions and the laser force throughout the duration of a 780nm laser pulse. Nonsequential ejection is shown to occur in a multi-electron, possibly multi-cycle and multi-dimensional, rescattering sequence that is coordinated by a number of sharp transverse recollimation impacts.Comment: 4 pages, 4 figure

Non-Sequential Double Ionization is a Completely Classical Photoelectric Effect

We introduce a unified and simplified theory of atomic double ionization. Our results show that at high laser intensities ($I \ge 10^{14}$ watts/cm$^2$) purely classical correlation is strong enough to account for all of the main features observed in experiments to date

Momentum Analysis in Strong-field Double Ionization

We provide a basis for the laser intensity dependence of the momentum distributions of electrons and ions arising from strong-field non-sequential double ionization (NSDI) at intensities in the range $I=1-6.5 \times 10^{14} W/cm^2$. To do this we use a completely classical method introduced previously \cite{ho-etal05}. Our calculated results reproduce the features of experimental observations at different laser intensities and depend on just two distinct categories of electon trajectories.Comment: 5 pages, 7 figure

Classical Effects of Laser Pulse Duration on Strong-field Double Ionization

We use classical electron ensembles and the aligned-electron approximation to examine the effect of laser pulse duration on the dynamics of strong-field double ionization. We cover the range of intensities $10^{14}-10^{16} W/cm^2$ for the laser wavelength 780 nm. The classical scenario suggests that the highest rate of recollision occurs early in the pulse and promotes double ionization production in few-cycle pulses. In addition, the purely classical ensemble calculation predicts an exponentially decreasing recollision rate with each subsequent half cycle. We confirm the exponential behavior by trajectory back-analysis

Energies and wave functions for a soft-core Coulomb potential

For the family of model soft Coulomb potentials represented by V(r) = -\frac{Z}{(r^q+\beta^q)^{\frac{1}{q}}}, with the parameters Z>0, \beta>0, q \ge 1, it is shown analytically that the potentials and eigenvalues, E_{\nu\ell}, are monotonic in each parameter. The potential envelope method is applied to obtain approximate analytic estimates in terms of the known exact spectra for pure power potentials. For the case q =1, the Asymptotic Iteration Method is used to find exact analytic results for the eigenvalues E_{\nu\ell} and corresponding wave functions, expressed in terms of Z and \beta. A proof is presented establishing the general concavity of the scaled electron density near the nucleus resulting from the truncated potentials for all q. Based on an analysis of extensive numerical calculations, it is conjectured that the crossing between the pair of states [(\nu,\ell),(\nu',\ell')], is given by the condition \nu'\geq (\nu+1) and \ell' \geq (\ell+3). The significance of these results for the interaction of an intense laser field with an atom is pointed out. Differences in the observed level-crossing effects between the soft potentials and the hydrogen atom confined inside an impenetrable sphere are discussed.Comment: 13 pages, 5 figures, title change, minor revision

Évaluation de l'âge et de la croissance de l'anguille européenne (Anguilla anguilla L.) en milieu continental : méthodologies, validation, application en Méditerranée et comparaisons en Europe

L'âge individuel de l'anguille en milieu continental est toujours un paramètre difficile à évaluer. Actuellement, seule l'otolithométrie est utilisée. Une description rapide des techniques de préparation et d'observation des otolithes, de leurs avantages et de leurs inconvénients, est donnée : observation in toto, ponçage, lames minces, brûlage, coloration, microscopie électronique à balayage, analyse chimique et analyse d'images. Elles sont axées sur l'interprétation des marques de croissance saisonnières. Malgré la diversité de ces méthodes, le choix d'une méthode fiable et universelle est difficile. De plus, les applications doivent être examinées et validées en fonction de chaque population de cette espèce dont la plasticité adaptative est remarquable. Les expériences de validation des estimations de l'âge (connaissance exacte des rythmes de dépôts de marques identifiées) à partir des otolithes sont peu nombreuses dans la littérature. Deux expériences de ce type sont présentées pour des populations méditerranéennes : une validation directe, par marquage individuel à la tétracycline dans un étang naturel de Camargue, et une validation indirecte, par observation de l'apparition marginale des marques de croissance au cours du temps pour des populations du Languedoc (étang saumâtre) et de Camargue (canal dulçaquicole). Ces expériences ont permis de déterminer précisément la séquence de formation des marques de croissance sur les otolithes ainsi que leur identification en fonction du mode de préparation. Une zone opaque large se forme principalement au printemps, une zone hyaline large se dépose pendant les mois estivaux, et une «ligne d'arrêt de croissance» chromophile correspond à la période hivernale. Ces marques sont donc utilisables pour estimer l'âge des anguilles en région méditerranéenne. Il existe cependant une très grande variabilité des structures de croissance, des rythmes de dépôt et de la morphométrie des otolithes. Cette variabilité est présente au niveau des individus de la même population mais aussi entre les populations. Ces résultats aboutissent à une notion d'écotype pour les otolithes d'anguille : l'écotype est en relation avec le milieu colonisé par l'individu et semble être fonction de la salinité et probablement du niveau trophique ; il retrace aussi l'histoire individuelle. Ces variabilités interviennent directement sur la croissance des individus. Les croissances individuelles dans les milieux méditerranéens saumâtre et dulçaquicole ont été mesurées et comparées entre elles et avec la littérature. La croissance en milieu saumâtre est nettement plus importante que celle en milieu d'eau douce

Plasticity of gene expression according to salinity in the testis of broodstock and F1 black-chinned tilapia, Sarotherodon melanotheron heudelotii

The black-chinned tilapia Sarotherodon melanotheron heudelotii Ruppell 1852 (Teleostei, Cichlidae) displays remarkable acclimation capacities. When exposed to drastic changes of salinity, which can be the case in its natural habitat, it develops quick physiological responses and keeps reproducing. The present study focused on the physiological impact of salinity on male reproductive capacities, using gene expression as a proxy of acclimation process. Two series of experimental fish were investigated: the first one was composed of fish maintained in freshwater for several generations and newly acclimated to salinities of 35 and 70, whereas the second one consisted of the descendants of the latter born and were raised under their native salinity. Expression patterns of 43 candidate genes previously identified from the testes of wild males was investigated in the three salinities and two generations. Twenty of them showed significant expression differences between salinities, and their predicted function revealed that most of them are involved in the osmotic tolerance of sperm cells and/or in the maintenance of sperm motility. A high level of expression variation was evidenced, especially for fish maintained in freshwater. In spite of this, gene expression patterns allowed the differentiation between fish raised in freshwater and those maintained in hypersaline water in both generations. Altogether, the results presented here suggest that this high variability of expression is likely to ensure the reproductive success of this species under varying salinities